ENGINE THROTTLE CONTROL FOR IMPROVED SHIFTING

COMMANDE DE GAZ DU MOTEUR POUR DES CHANGEMENTS DE VITESSE AMELIORES

English Abstract

A vehicle includes a powershift transmission driven by an electronically
controlled
engine. A control system momentarily modifies a magnitude of an engine
throttle command
signal during a shift of the power shift transmission in order to make the
shift smoother and
less sensitive to achieving optimum clutch engagement pressure. It also
prevents an engine
governor from over-reacting and causing rough shifts.

Claims

The embodiments of the invention in which an exclusive property or privilege
is claimed are
defined as follows:
1. A control system for a vehicle having an engine 10 which drives a power
shift
transmission, the power shift transmission having a gear box which is operated
by a set of
pressure operated clutches which are controlled by a corresponding set of
solenoid operated
shift control valves which are controlled by an electronic vehicle control
unit (VCU) in
response to the shift command signals generated by an operator controlled
shift control lever
mechanism, the engine being controlled by an electronic engine control unit
(ECU) which
receives a throttle command signal from the VCU, comprising:
a throttle command modifier for modifying a magnitude of the throttle command
signal during a shift of the power shift transmission.
2. The control system of claim 1, wherein:
the throttle command modifier momentarily modifies the magnitude of the
throttle
command signal during said shift.
3. The control system of claim 1, wherein:
during said shift, the throttle command modifier abruptly modifies the
magnitude of
the throttle command signal and then gradually returns the magnitude of the
throttle
command signal back to its original magnitude upon completion of said shift.
4. The control system of claim 1, wherein:
during an upshift of the power shift transmission, the throttle command
modifier
reduces the magnitude of the throttle command signal.
5. The control system of claim 4, wherein:
the throttle command modifier momentarily reduces the magnitude of the
throttle
command signal during said upshift.
6. The control system of claim 4, wherein:
during said upshift, the throttle command modifier abruptly reduces the
magnitude of
the throttle command signal and then gradually increases the magnitude of the
throttle
command signal back to its original magnitude prior to said upshift.
7. The control system of claim 1, wherein:
during a downshift of the power shift transmission, the throttle command
modifier
increases the magnitude of the throttle command signal.
8. The control system of claim 7, wherein:
the throttle command modifier momentarily increases the magnitude of the
throttle


command signal during said downshift.
9. The control system of claim 7, wherein:
during said downshift, the throttle command modifier abruptly increases the
magnitude of the throttle command signal and then gradually decreases the
magnitude of
the throttle command signal back to its original magnitude prior to said
downshift.
10. The control system of claim 1, wherein:
the throttle command signal is modified to a value which produces a modified
engine
speed corresponding to a change in a gear ratio resulting from the shift.
11. The control system of claim 10, wherein:
during an upshift, the throttle command signal is reduced to a value which
produces
a lower engine speed corresponding to a change in a gear ratio resulting from
the upshift.
12. The control system of claim 10, wherein:
during a downshift, the throttle command signal is increased to a value which
produces a higher engine speed corresponding to a change in a gear ratio
resulting from the
downshift.
13. In a vehicle having an engine which drives a power shift transmission, the
power shift transmission hawing a gear box which is operated by a set of
pressure operated
clutches which are controlled by a corresponding set of solenoid operated
shift control
valves which are controlled by an electronic vehicle control unit (VCU) in
response to the
shift command signals generated by an operator controlled shift control lever
mechanism,
the engine being controlled by an electronic engine control unit (ECU) which
receives a
throttle command signal from the VCU, a method of improving shift quality
comprising:
modifying a magnitude of the throttle command signal during a shift of the
power shift
transmission 12.
14. The method of claim 13, wherein:
the magnitude of the throttle command signal is momentarily modified.
15. The method of claim 13, wherein:
during said shift, the magnitude of the throttle command signal is abruptly
modified
and then gradually returned back to its original magnitude upon completion of
said shift.
16. The method of claim 13, wherein:
during an upshift of the power shift transmission, the throttle command
modifier
reduces the magnitude of the throttle command signal.
17. The method of claim 16, wherein:
the magnitude of the throttle command signal is momentarily reduced during
said



upshift.
18 The method of claim 16, wherein:
during said upshift, the magnitude of the throttle command signal is abruptly
reduced
and then gradually increased back to its original magnitude prior to said
upshift.
19. The method of claim 13, wherein:
during a downshift of the power shift transmission, the magnitude of the
throttle
command signal is increased.
20. The method of claim 19, wherein:
the magnitude of the throttle command signal is momentarily increased during
said
downshift.
21. The method of claim 19, wherein:
during said downshift, the magnitude of the throttle command signal is
abruptly
increased and then gradually decreased back to its original magnitude prior to
said
downshift.
22. The method of claim 13, wherein:
the throttle command signal is modified to a value which produces a modified
engine
speed corresponding to a change in a gear ratio resulting from the shift.
23. The method of claim 22, wherein:
during an upshift, the throttle command signal is reduced to a value which
produces
a lower engine speed corresponding to a change in a gear ratio resulting from
the upshift.
24. The method of claim 22, wherein:
during a downshift, the throttle command signal is increased to a value which
produces a higher engine speed corresponding to a change in a gear ratio
resulting from the
downshift.

Description

CA 02302786 2000-03-28
ENGINE TI-IROTTLE CONTROL FOR IMPROVED SHIFTING
Background of the Invention
The present invention relates to a vehicle powershift transmission and engine
control
system.
Powershift transmissions change speeds by disengaging one or more clutches and
then engaging one or more clutches, with no interruption of power during the
shift. Shift
smoothness is obtained by modulating the pressure of the oncoming clutches,
i.e. engaging
them at low pressure. Shift smoothness is very sensitive to having the optimum
engagement pressure in relation to the load being transmitted by the
transmission. If the
engagement pressure is too low, the vehicle may drop load or speed during the
shift, if the
engagement pressure is too high, the shift will be aggressive, jumpy and
harsh. Under
lightly loaded conditions, the typical engine governor response contributes to
the poor shift.
For example, during an upshift, if the engaging clutch locks up quickly, it
will bring the engine
speed down rapidly. The engine governor typically over-reacts to this drop in
speed by
quickly increasing fuel to the engine. An excess amount of fuel may then cause
the engine
to quickly overshoot the cornmanded speed. The resulting acceleration-
deceleration causes
the vehicle to pitch fore and aft, and produces a "jumpy" feel.
Summary of the Invention
Accordingly, an object of this invention is to provide a transmission and
engine
control system which prevents such engine governor-caused rough shifts.
Accordingly, another object of this invention is to provide a transmission and
engine
control system which makes shift smoothness less sensitive to modulating the
oncoming
clutch at the optimum pressure.
These and other objects are achieved by the present invention, wherein a
control
system for a vehicle is provided. The vehicle includes an engine which drives
a powershift
transmission. The powershift transmission has a gear box which is operated by
a set of
pressure operated clutches which are controlled by a corresponding set of
solenoid operated
shift control valves. The valves are controlled by an electronic vehicle
control unit (VCU) in
response to the shift command signals generated by an operator controlled
shift control lever
mechanism. The engine is controlled by an electronic engine control unit (ECU)
which
receives a throttle command signal from the VCU. During an upshift the control
system
depressurizes at least one off-going clutch and later pressurizes at least one
on-going
clutch. The VCU, during a shift, abruptly modifies the magnitude of the
throttle command
signal while the off-going clutch is being de-pressurized, and then gradually
returns the
magnitude of the throttle command signal back to its original magnitude when
the on-going
clutch is fully pressurized. During an upshift, the throttle command signal TC
is similarly
momentarily decreased at the start of the clutch swap, and is then gradually
increased or


CA 02302786 2000-03-28
ramped up. During a downshift, the throttle command signal TC is similarly
momentarily
increased at the start of the clutch swap, and is then gradually decreased or
ramped down.
This strategy allows the engine to accomplish most of the change in vehicle
speed, and is
less dependent on proper slipping of the oncoming clutch. This also causes the
engine
governor to react properly to the shift, and avoids governor over-reaction.
Brief Description of the Drawings
Fig. 1 is a simplified schematic diagram of a vehicle transmission/engine
drive and
control system of the present invention; and
Figs. 2 is a signal tirning diagram illustrating the time behavior of the
throttle
command signal in relation to the operation of the transmission control
clutches.
Description of the Preferred Embodiment
As shown in FIG. 1, a vehicle power train includes an engine 10 which drives a
power shift transmission 12, which has an output shaft 13 which is connected
to drive
wheels (not shown). The power shift transmission 12 includes a transmission or
gear box 18
which is operated by a set of pressure operated control elements or clutches
20 which are
controlled by a corresponding set of solenoid operated shift control valves
22. The
transmission 18 is preferably a powershift transmission such as a production
John Deere 16
speed powershift transmission, which is controlled by an electronic vehicle
control unit
(VCU) 14, or such as described in U.S. Pat. No. 5,011,465, issued 30 Apr. 1991
to Jeffries et
al., and assigned to the assignee of this application. The engine 10 is
preferably an
electronically controlled engiine such as a production John Deere 8.1 liter
Diesel engine, and
is controlled by a production electronic engine control unit (ECU) 16.
The VCU 14 sends shift control signals to the shift control valves 22 in
response to
command signals it receives from an operator controlled shift control lever
mechanism 24,
such as the shift control mechanism of a production John Deere 8000 Series
tractor. For
example, Fig. 2 shows the behavior of the pressure (P-OFF) of an off-going
clutch and
P-ON of an on-going clutch during a typical upshift.
According to the present invention, the VCU 14 controls or modifies the
throttle
command signal during upshifts and downshifts to improve the quality or
smoothness of
shifts. As best seen in Fig. 2, the VCU 14 momentarily reduces the magnitude
of the throttle
command signal during an upshift of the power shift transmission 12. More
specifically,
during an upshift, the magnitude of the throttle command signal, TC, is
abruptly reduced
when the pressure of the ofi~-going clutch, P-OFF, is being reduced to zero.
Preferably, the
throttle command signal TC is reduced to a value which would produce a lower
engine
2


CA 02302786 2000-03-28
speed corresponding to the change in gear ratio resulting from the upshift.
Thereafter, the
magnitude of the throttle command signal TC is gradually increased as the
pressure P-ON of
the on-coming clutch is gradually increased, and so that the magnitude of the
throttle
command signal TC is bacH; up to its original magnitude when the on-going
clutch pressure
P-ON is at its full on pressure level.
Similarly, although not illustrated, for a downshift, the throttle command
signal TC
momentarily increased at the start of the clutch swap, and is then gradually
decreased or
ramped down.
While the present invention has been described in conjunction with a specific
embodiment, it is understood that many alternatives, modifications and
variations will be
apparent to those skilled in the art in light of the foregoing description.
Accordingly, this
invention is intended to embrace all such alternatives, modifications and
variations which fall
within the spirit and scope of the appended claims.
3

Representative Drawing